.jd_layout {
    width: 100%;
    max-width: 640px;
    min-width: 320px;
    margin: 0 auto;
    background-color: white;
}
 
/* 顶部搜索块 */
.jd_search {
    width: 100%;
    height: 40px; 
    max-width: 640px;    
    /* 固定布局 */
    position: fixed;
    background-color: rgba(255, 0, 0, 0);
    z-index: 9999;
}
.jd_logo {
    width: 68px;
    height: 33px;
    display: block;
    position: absolute;
    top: 6px;
    background: url(../img/jd_logo.png) no-repeat;
    background-size: 67.5px auto;
}
.jd_login {
    height: 38px;
    line-height: 40px;
    width: 40px; 
    position: absolute;
    top: 0;
    right: 0;  
    color: white;
    text-align: center;
    margin-top: 2px;
}
.jd_searchBox {
    width: 100%;
    height: 100%;
    padding-left: 68px;
    padding-right: 40px;
}
.jd_searchBox  input {
    width: 100%;
    margin-top: 10px;
    height: 25px;
    border-radius: 12.5px;
    padding-left: 10px;
    opacity: .9;
}
.jd_searchBox::before {
    content: "";
    position: absolute;
    /* 可以加一个logo(放大镜) */
}

/* 搜索框的大小 */
.position_top {
    top:40px;
}
